The initiating system consisting of AlCl3 with dialkyl ether such as di-n-butyl ether or diisopropyl ether has been successfully developed for providing a cost-effective process of synthesis of highly reactive polyisobutylenes (HRPIBs) with large proportion of exo-olefin end groups up to 93 mol% at temperatures ranging from -20 to +20 degrees C. The above dialkyl ethers played very important roles in promoting the directly rapid beta-proton elimination from -CH3 of the growing chain ends to create exo-olefin end groups and decreasing or even suppressing the carbenium ion rearrangements to form the double bond isomers. Very importantly, the highly reactive PIBs with 80-92 mol% of exo-olefin end groups, having low M(n)s of 1300-2300 g mol(-1) and monomodal molecular weight distribution (M-w/M-n = 1.7-2.0) could be achieved at 0-20 degrees C. These results are comparable to those of commercial HRPIBs produced industrially by the best BF3-based initiating system at far below 0 degrees C. (C) 2010 Published by Elsevier Ltd.